The present invention relates to a magnetic disk drive and, more particularly, to a magnetic disk drive adapted to move a magnetic head to a target track.
A magnetic disk drive that is a storage device external to a computer has a magnetic head that moves to a target track on a surface of a rotating magnetic disk to perform recording and playback of data.
Generally, a following control system for causing a magnetic head to keep track of the same track to read and write data, a seek control system for moving the magnetic head to a target track where data is present, and a settling control system for performing a splice from the seek control system to the following control system near the target track are present in a magnetic head positioning control system.
In the seek control system, at relatively short seek spans, the control input does not saturate during acceleration. Also, the upper limit of the moving velocity is not exceeded. Therefore, a two-degree-of-freedom control system using a smooth acceleration trajectory relying on a time function can be applied. In this two-degree-of-freedom control system, vibrations produced during a seek operation can be suppressed. Another advantage is that a position feedback system having good error rejection characteristics can be used.
In the two-degree-of-freedom control system relying on a time function, a target acceleration given as a feedforward control input and a method of how the target position or target velocity is given to the feedback system are important design components.
In JP-A-2000-233609 (Patent Reference 1), a method of realizing a target acceleration by a time function of the third order is disclosed. In this method, the target velocity is derived as a quartic function obtained by integrating a time function used in the target acceleration. The target position is derived as a quintic equation obtained by integrating a velocity trajectory.
In JP-A-5-143165 (Patent Reference 2), a method of realizing a velocity trajectory by a time function of the fifth order is disclosed. At this time, the target acceleration trajectory is derived from a quartic function obtained from differentiating the velocity trajectory. The target position is derived from a sextic function obtained by integrating the velocity trajectory.
In JP-A-123502 (Patent Reference 3), a method is disclosed in which a target acceleration is taken as a sine wave where the time is an input. The velocity trajectory is realized by integration of the acceleration trajectory. The position trajectory is realized by integration of the velocity trajectory.